FIELD OF THE INVENTION
This invention relates to a method of preparing promoted vanadium antimony oxide catalysts useful in catalytic hydrocarbon ammoxidation to .alpha., .beta.-unsaturated mononitriles; i.e., acrylonitrile and methacrylonitrile, catalytic oxidation, and NO.sub.x reduction. In particular, the process of the present invention provides promoted VSbO.sub.x catalysts useful in the ammoxidation of propane to acrylonitrile.
Because of the price differential between propylene and propane an economic incentive exists for the development of a viable catalytic process for conversion of propane to acrylonitrile.
Earlier attempts in the prior art to develop an efficient process for the ammoxidation of propane to acrylonitrile produced either insufficient yields or processes that necessitated adding halogen promoters to the feed. The latter procedure would require not only reactors made of special corrosion resistant materials, but also the quantitative recovery of the promoter. The added costs thus eliminated the advantage of the propane/propylene price differential.
In U.S. Pat. No. 3,860,534 there are disclosed catalysts for the ammoxidation of propane (or other alkanes) using an excess of propane to both ammonia and molecular oxygen wherein the ranges of the paraffin to NH.sub.3 and to O.sub.2 overlap the ranges of the present process. The catalyst may be mixed with particles of an inert and refractory material, or applied as a layer on the surface of an inert support. Except for such inert materials, the catalyst contains only V, Sb and oxygen. The catalyst is calcined at 350.degree. to 950.degree. C., preferably 700.degree. to 900.degree. C., and particularly 750.degree. to 870.degree. C., and most desirably 790.degree. to 850.degree. C. The essence of the invention is that before use the catalyst is water-washed for long periods in water.
Earlier (earlier filed in the priority country) British patent specification No. 1,336,135, having a common assignee and a common inventor with the aforesaid U.S. patent, discloses inter alia the use of catalysts containing only V and Sb in oxidic form in the ammoxidation of paraffins such as propane at the same alkane to NH.sub.3 and O.sub.2 ratios, the catalysts being calcined at 300.COPYRGT.to 950.degree. C., preferably 600.degree. to 850.degree. C. However, the calcined catalysts are not water-washed. The earlier specification also discloses that the catalysts can contain V and Sb and only one other metal. The sole third component disclosed for addition to a V, Sb catalyst is tin, and this is only by way of specific Example III.
U.S. Pat. No. 4,746,641, Guttmann et al. discloses ammoxidation of paraffins including propane and isobutane at ratios of reactants different than the present claims using catalysts that can contain Sn in addition to V and Sb.
British Patent No. 1,336,136, another earlier patent to the common assignee and to a sole inventor who is the common inventor in British Patent No. 1,336,135 and U.S. Pat. No. 3,860,534 is much the same as British Patent No. 1,336,135 but more narrow. Thus, all of the catalysts contain V and Sb in oxidic form with or without only one other metal. The only such other metal identified is tin, which is in Example III, identical to Example III of British No. 1,336,135, already discussed.
Canadian patent No. 901,006 also relates to ammoxidation of propane and isobutane using catalysts of seven different categories. The only pertinent category uses exactly three metals in oxidic form in combination, exclusive of the combination V-Sb-Sn. The three are chosen from Sb, Sn, Ti, V and U. No proportions are suggested, except in specific examples. No specific suggestion of, or specific example of, a catalyst having V, Sb and Ti is disclosed.
Recent U.S. Pat. Nos. 4,784,929, 4,879,264, 5,008,427 and 5,094,989, all assigned to the assignee of the instant application disclosed various procedures for preparation of VSbO.sub.x catalyst or VSbO.sub.x promoted catalyst useful in the ammoxidation of propane to acrylonitrile.